1. Field of the Invention
This invention relates to a method for forming a semiconductor device, more particularly to a method for forming a semiconductor device that involves forming a single crystal scandium oxide (Sc2O3) film on a silicon (Si) substrate through electron beam evaporation techniques using a Sc2O3 powder source.
2. Description of the Related Art
Heteroepitaxy and heterogrowth of a semiconductor film between an insulator layer and a semiconductor substrate have always attracted a lot of interest in scientific research and development, and industrial applications.
Formation of compound semiconductors on a substrate is an important application of the heteroepitaxy techniques. One attention-grabbing example is epitaxial growth of compound semiconductors of GaN series on a sapphire substrate. The layered structure of GaN/sapphire has been used in the manufacture of a blue or green light emitting diode. However, since the sapphire substrate has a poor heat-dissipating property and is relatively expensive, application of the sapphire substrate to light emitting devices having a relatively large size is limited. In addition, since the sapphire substrate has a relatively high hardness, the yield of the light emitting devices during subsequent grinding and cutting operations is relatively low, whereas the production cost of the same is relatively high.
However, the most difficult barrier to growth of an epitaxial film on a substrate is that the epitaxial film has to match the substrate in lattice constant so as to avoid occurrence of lattice defects, or even chip bending, due to stress.
Recently, growth of an epitaxial film of a compound semiconductor indirectly on a Si substrate through an insulating oxide film has been realized, which opens the possibility to replace the sapphire substrate with the Si substrate.
M. Hong et al. have described a heterostructure including a sapphire substrate, a first GaN film, an interfacial film made from Gd2O3 or Y2O3 and epitaxially grown on the first GaN film, and a second GaN film epitaxially grown on the interfacial film (“Single-crystal GaN/Gd2O3/GaN heterostructure,” J. Vac. Sci. Technol. B 20(3), May/June 2002, pp. 1274 to 1277). It has been found that despite a large mismatch in the lattice constant, Gd2O3 or Y2O3 can be epitaxially grown on the single-crystal GaN film, thereby permitting epitaxial growth of a GaN film thereon. The GaN film grown on the Gd2O3 or Y2O3 film has the same crystallographic hexagonal close-packed (hap) structure as the underlying GaN film.
Formation of a Sc2O3 epitaxy film on a Si substrate is conventionally conducted by using metal scandium (Sc) as the source material in an evacuated chamber. When Sc is heated to form evaporated Sc atoms, an oxygen gas is injected into the evacuated chamber to react with the evaporated Sc atoms to form compound Sc2O3. The compound Sc2O3 is then deposited on the Si substrate. However, the Sc2O3 film thus deposited on the Si substrate is not a single domain film, and has a poor crystallization quality, which can result in a relatively high defect density in the compound semiconductor epitaxially grown thereon, and which can deteriorate performance of the electronic devices manufactured therefrom
Therefore, there is still a need in the art to provide a method for forming a single crystal Sc2O3 film of improved crystallization quality on a Si substrate.